| Watermelon (Citrullus lanatus Mansfeld) is the world’s major vegetable, and is also one of the principal fruit crops which has the largest planting area and is most widely cultivated in China. Impact of soil salinity has become a major factor that affects the yield and quality of watermelon, it is a serious impediment to the sustainable development of watermelon’s facility cultivation, and grafting is an important technology to overcome soil salt. In this paper, the influence of grafting to watermelon seedlings under salt stress and physiological responses is studied, furthermore, the physiological and biochemical mechanism through which grafting improves the salt tolerance ability of watermelon seedlings is explored, and the following results are achieved:(1) Using nutrient solution for culture, choosing ’super-abundance of antibiotic King’, ’General’,’Fengyuan Pioneer’,’South anvil 1’,’Green anvil 1’,’Gourd’ as rootstock,’the ruby in early spring’,’beauty’ as scion,we have studied the effect of the treatment of 200 mmol·L-1 NaCl on the salt tolerance ability of the rootstock and the affinity between the rootstock and the scion. The results showed that under salt stress, the excellent strain rates of pumpkin rootstock general, super abundance of antibiotic Wang were separately 94% and 92%, and they the ideal grafting stock material;The grafted seedlings of the combination of super-abundance of antibiotic King/beautiful, general/beautiful have the survival rates of 93.6% and 90.5% under salt stress, for the ideal grafting combination, which can be used for the grafting cultivation of facility watermelon.(2) Using nutrient solution for culture, choosing the ’super-abundance of antibiotic King’ gourd as rootstock,’beautiful’watermelon as the scion, we have studied the effect of a salt stress on the Antioxidant Systems of self-rooted and grafted watermelon. The results showed that under salt stress, the leaves’ H2O2, MDA content and membrane’s relative permeability of self-rooted and grafted watermelon was significantly increased, the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) was significantly increased, the content of AsA and GSH were significantly reduced;but the increasing extent of the leaves’ H2O2, MDA content and membrane’s relative permeability of grafted watermelon and the decreasing extent of AsA, GSH content were both less than self-rooted seedlings, and the increasing rate of antioxidant enzyme activity was more than self-rooted seedlings. It showed that grafting can significantly enhance plants’ ability of eliminating active oxygen, which can reduce the extent of lipid peroxidation, and increase the salt tolerance ability of watermelon seedlings.(3) Using watermelon seedlings as materials, we have studied the effect of grafting on watermelon seedlings chlorophyll (Ch) content and gas exchange parameters under NaCl stress. The results showed that:under NaCl stress, with treatment time prolonging, the decreasing extent of Ch a, Ch b, total Ch content, and ratio of Ch a/Ch b in grafted watermelon seedlings was less than that in self-rooted seedings. Under salt stress, Pn, Gs, Ci, and Tr of self-rooted and grafted seedlings were all significantly lower, but Ls was significantly increased, and all these indicators were to reach a very significant level at the eighth day. Compare with self-rooted seedlings, grafting could decrease the extent of Ls significantly, and increase Pn. These results showed that grafting could lighten the photosynthesis inhibition, and improve the photosynthetic rate of watermelon seedlings under salt stress.(4) Using watermelon seedlings as materials, we have studied the effect of grafting on watermelon seedlings chlorophyll fluorescence and the chloroplast ultrastructure under NaCl stress. The results showed that, under NaCl stress, with treatment time prolonging, the decreasing extent of Fv/Fm, Fv’/Fm’,ΦPSⅡ, qP, qN, and rETR in grafted watermelon seedings was less than that in self-rooted seedlings. Transmission electron microscopy observation indicated that, under NaCl stress, the chloroplast lamellae structure in self-rooted seedings presented loose, and stroma lamellae arranged disorderly, and plastoglobuli increased. Compare with self-rooted seedlings, the chloroplast lamellae structure in grafted watermelon seedings was better, and the photosynthetic membrane still kept completeness. The test showed that, under salt stress, grafting could play a significant role in protecting the photosynthetic membrane of watermelon, protect watermelon PSⅡ, enhance the primary light to energy conversion efficiency of its PSⅡand can promote the primary reaction process of photosynthesis, thus contributing to photosynthesis.(5) Using nutrient solution for culture, conducting NaCl salt stress treatment, and using the gourd rootstock which has stronger salt tolerance ability to graft watermelon,having studied the effect of grafting on the Na+, K+ content of graftet watermelon seedlings’root segment and overground segment, various parts of root tissues under salt stress. The results showed that the grafted watermelon seedlings intercepted more Na+ in underground part than in overground part, while the K+ content of overground part was significantly higher than that of the underground;the ability of grafted seedlings’root closure of Na+ and the above-ground absorbtion of K+ is stronger than self-rooted.Those explained that graftet watermelon seedlings can separate the transportation of Na+ from roots’inner cortex to the column tube and limit the loading of Na+ to the column tube, and then intercepted Na+ more in the roots and prevent it from transporting to the overground;while transporting K+ more to the overground part, maintaining a high [K+]/[Na+] ratio in the overground part, thereby maintaining a strong salt tolerance ability of grafted watermelon. |
PDF Full Text Request